A fall is defined as a sudden, uncontrolled and unintentional downward displacement of the body to the ground. Falls affect millions of people every year and result in significant injuries, particularly in the elderly. In fact, falls have been estimated to be among the top three causes of death in elderly people.
There are currently some fall detection apparatus available that detect these falls and allow the user to obtain assistance manually or automatically if a fall occurs. One example of a fall detection apparatus detects falls in accordance with the velocity profile of a user in the vertical direction, since a vertical body movement in the direction of gravity occurs during the fall. If the maximum velocity in the direction of gravity is larger than a threshold, it is determined in such an apparatus that a fall occurs.
However, this threshold is only suitable when the accelerometer is worn on the torso. If the sensor is worn on the wrist, other activities, such as waving or shaking hands, may also involve wrist movement at a velocity as high as falls. Therefore, the maximum velocity cannot be used as a reliable feature to distinguish falls from other activities.
Thomas Degen et al. (see “Speedy: a Fall Detector in a Wrist Watch”, Proceedings of the Seventh IEEE International Symposium on Wearable Computers (2003), Page(s): 184-187, the contents thereof are herein incorporated by reference) proposed a wrist-worn fall detector for elderly people. It is compact and easy to use.
However, this detector still uses the simple criteria of determining whether a fall occurs if the maximum velocity is larger than a predetermined threshold (in the above document, the velocity threshold for fall detection is 1.3 ms−1). Since the hands play a very important role in our daily lives, this detection method usually results in a false alarm in activities in which the velocities of hands are larger than the threshold, for example, in handshaking.